Molding is a process whereby raw plastic or polymeric pellets are transformed into molded articles by way of an extruder that plasticizes the raw pellets and forces them into the mold, or through a die, that defines the shape of the article(s) being produced. Raw plastic pellets are gravitationally feed to the extruders' plasticizing assembly by a feed assembly that includes a hopper, which is coupled directly to the extruder, or is coupled to the extruder by a tubular passageway. Often, gravity alone is sufficient for ensuring a reliable, or stable, flow of pellets between the feed assembly and the plasticizing assembly; however, in some applications, the pellets have a tendency to interlock and impede the flow of pellets between the feed assembly and the plasticizing assembly. This phenomenon, known in the art as “bridging”, results in the flow of plastic pellets becoming restricted, or even stopped altogether.
To prevent restrictions to the gravitational flow of pellets an operator can monitor the feed and flow of pellets in the feed assembly and manually clear any blockage as it begins to accumulate. However, this solution requires human intervention, and is therefore prone to inconsistencies, and is also only suitable when the operator has access to the stoppage or bridging area.
Vibrators have been coupled to the feed assembly at a location proximate to the suspected bridging area in order to vibrate the tubular passageway within which the “bridged” pellets are located. In some applications this solution has a tendency to exacerbate the problem by tightly compacting and interlocking the pellets in the bridging zone, again requiring operator intervention to clear the blockage.
Another solution has been to mount a cylindrical rod to extend within the feed assembly that is connected to a source of vibration that is external to the flow of pellets. In some applications, this solution has the tendency to compact and interlock the pellets between the rod and the internal walls of the feed assembly.
Another solution has been to mount a linear actuator within the feed assembly at a potential blockage point to “stab” at pellets to prevent them from interlocking. This solution is only practical in locations of the feed path that are large enough to accommodate a linear actuator within the flow of pellets, and may also cause a blockage of pellets upstream from the linear actuator.
Another solution has been to rotate an auger within the feed path. However this solution requires a relatively complex assembly to power the auger, and is only practical in applications where the feed assembly can accommodate an auger.